1. Field of the Invention
The present invention relates to a semiconductor device with enhanced visual identifiability of a joining agent deposited on external terminals, and to a method of manufacturing the semiconductor device.
2. Description of the Related Art
In response to recent demands for smaller and slimmer semiconductor devices, nonleaded semiconductor devices have been proposed such as VQFN (Very Thin Quad Flat Nonleaded Package) and VSON (Very Thin Small Outline Nonleaded Package) in which external terminals are exposed from the package bottom surface. See Japanese patent application Laid-open Publication No. 2003-31753.
FIG. 14 is a perspective view showing a mounting surface of a conventional VQFN semiconductor device 100. As shown in this figure, a plurality of external terminals (bonding pads) 106 are exposed at given pad pitches on a circumferential portion of the mounting surface of the conventional semiconductor device 100.
FIG. 15 is a sectional view showing the mounting condition of the conventional semiconductor device 100 to a printed wired board 200. An upper surface portion of the printed wired board 200 is coated with a solder resist 201 to prevent a joining agent 300 such as solder from being deposited on any portions other than conductive pattern. Portions not coated with the solder resist 201 serve as lands 202 as conductive pattern.
In such a case, the external terminals 106 of the conventional semiconductor device 100 are joined via the joining agent 300 to the lands 202 of the printed wired board. It is to be noted that spacings between the external terminals 106 (pad pitches) have been made narrower in response to demands for finer pitches (narrower pad pitches), thus rendering the adjacent external terminals 106 more vulnerable to a so-called solder bridge by which the joining agent 300 deposited on each of the external terminals 106 overlaps with each other. To prevent this solder bridge, the amount of the joining agent 300 deposited on the external terminals 106 is kept to a minimum.
Incidentally, following mounting of the semiconductor device to the printed wired board, fillets (shapes) of the joining agent 300 formed between the external terminals 106 and the lands 202 are shown on monitor using a CCD camera or something similar provided in a given inspection device. Based on the image shown on a monitor, a pass/fail judgment is made through visual check on the joining condition of the external terminals 106 and the lands 202 via the joining agent 300.
In the case of nonleaded semiconductor devices such as VQFN, however, the external terminals 106 are arranged exposed on the mounting surface (package's rear surface), with the amount of the joining agent 300 kept to a minimum for finer pitches. This results in difficulties in visually checking the shape of the joining agent 300, thus making a pass/fail judgment difficult on the joining condition of the external terminals 106 and the lands 202.